1. Field of the Invention
The present invention relates to bio-based monomers derived from non-petroleum celluloses or carbohydrates with a core scaffold of isosorbide, isomannide or isoidide, and their use for producing renewable vinyl resin systems.
2. Description of the Related Technology
Vinyl ester resins are thermosetting polymers that are commonly used in variety of applications ranging from adhesives to the resin matrices for fiber reinforced composites. There are many desirable features for vinyl ester resins, such as strength, toughness, low cost, low weight, and particular viscosities for processing, which are the reasons that vinyl ester resins have such wide acceptance in military and commercial uses.
Viscosity is a key factor for determining the utility of vinyl ester resins because lower viscosity resins are easier to work with and may be prepared using a larger range of methods. Petroleum-based vinyl ester resins are typically high molecular weight species that are often an extremely viscous fluids or solids. They require reactive diluents in order to reduce the resin viscosity so that the resins can be processed. Typical reactive diluents, such as styrene, are generally regarded as Hazardous Air Pollutants (HAPs) and/or Volatile Organic Compounds (VOCs) whose use is controlled by the Environmental Protection Agency (EPA). Large research efforts have been devoted to finding ways to eliminate or reduce the use of these highly hazardous reactive diluents.
Another factor that prevents vinyl ester resins' wider commercial use is that they are frequently derived from petroleum products. Petroleum is a commodity with well-known price volatility. The environmental costs of using petroleum are also very high.
Vinyl ester resins derived from renewable sources cam reduce dependency on petroleum and have quickly become an imperative for continued use and development of thermosetting polymers and composites. Bio-refining of material based on converting biomass into vinyl ester products has been successfully developed. For example, bio-refining of triglycerides and carbohydrates have produced a wealth of new fine chemicals that are useful for the development of bio-based polymers. Fatty acids and triglycerides have also been successfully developed into materials ranging from toughening agents and plasticizers to reactive diluent replacements.
U.S. Pat. No. 6,121,398 (Wool et al.) discloses functionalized triglycerides derived from plant oil that are polymerizable and their use to produce high modulus polymers. The functionalized triglycerides may be produced via several different chemical synthesis routes. For example, epoxidized triglyerides may be produced and converted to resilient rubbers by control of the molecular weight and cross-link density. The resultant rubbers can be used as rubber toughening agents in rigid composites. In the examples of this patent, acrylated base resins are prepared by reacting the epoxidized triglycerides with acrylic materials such as acrylic acid. The thermosetting resins prepared by this method are said to have properties similar to commercially available bisphenol-A vinyl ester resins. Other functionalized triglycerides are described in U.S. Pat. No. 6,825,242 and U.S. patent application publication nos. US 2003/0139489 and US 2009/0275715.
Besides triglycerides, anhydrosugars derived from cellulose or carbohydrates, such as isosorbide, isomannide and isoidide, have also been explored for use as reactive monomers. These anhydrosugars are useful building blocks because they provide a rigid bicyclic core structure that can be developed into resins. For example, anhydrosugar, or bis-anhydrohexitols, have been fashioned into epoxy resins by forming the corresponding glycidyl ethers, as described in U.S. Pat. No. 3,041,300 (Zech, et al.) and U.S. Pat. No. 3,272,845 (Morrison, et al.). U.S. Pat. No. 7,619,056 (Jaffe, et al.) describes a different synthesis process whereby the glycidyl ethers of these anhydrosugars can be obtained, and subsequently cured with polyamines to form thermosets.
However, anhydrosugars have not been successfully used to produce low viscosity thermosetting vinyl ester resins. Reactive diluents such as styrene are still commonly used for reducing viscosity of these bio-based resins. Commercial practice involves reducing the styrene content in the resin to about 33 wt % styrene, which makes the resin barely acceptable for composite manufacturing applications. In addition, reducing the styrene content significantly reduces the toughness of these resins.
Therefore, there is a need in the field to provide bio-based vinyl ester resins with excellent processabilty, acceptable toughness and a reduced dependency on reactive diluents.